Here's how wildfires get started—and how to stop them

In the United States, fire season lasts from June through September. Here’s what you need to know as seasonal winds drive flames across the country.

Climate 101: Wildfires

Here's how wildfires get started—and how to stop them

In the United States, fire season lasts from June through September. Here’s what you need to know as seasonal winds drive flames across the country.

Climate 101: Wildfires

Wildfires can burn millions of acres of land at shockingly fast speeds, consuming everything in their paths. These rolling flames travel up to 14 miles an hour, which converts to about a four-minute-mile pace, and can overtake the average human in minutes.

In 2020, the wildfire season in the United States—which lasts from June through September—promises to be particularly devastating. This summer is expected to be the hottest on record, with drought conditions predicted in California through September. In addition, the COVID-19 pandemic has derailed mitigation efforts—such as homeowner assistance programs and controlled burns—due to concerns over social distancing and respiratory dangers. By the end of June, the California Department of Forestry and Fire Protection had responded to nearly double the number of fires than it had in the entire 2019 season.

Destruction caused by wildfires in the United States has significantly increased in the last two decades. An average of 72,400 wildfires cleared an average of 7 million acres of U.S. land each year since 2000, double the number of acres scorched by wildfires in the 1990s. In 2015, the largest wildfire season recorded in U.S. history burned more than 10 million acres of land.

Because much of the U.S. is expected to get hotter and drier with climate change, wildfire risk is generally expected to rise. At the same time, as the population in the United States rises and people increasingly move into rural and wilderness areas, more homes and other structures are likely to be placed in harm’s way. That’s why it’s critical to understand how wildfires get started, how to stop them, and what to do when they occur.

How wildfires start

Though they are classified by the Environmental Protection Agency as natural disasters, only 10 to 15 percent of wildfires occur on their own in nature. The other 85 to 90 percent result from human causes, including unattended camp and debris fires, discarded cigarettes, and arson.

Naturally occurring wildfires can spark during dry weather and droughts. In these conditions, normally green vegetation can convert into bone-dry, flammable fuel; strong winds spread fire quickly; and warm temperatures encourage combustion. With these ingredients, the only thing missing is a spark—in the form of lightning, arson, a downed power line, or a burning campfire or cigarette—to wreak havoc.

Natural or man-made, three conditions must be present for a wildfire to burn: fuel, oxygen, and a heat source. Firefighters call these three elements the fire triangle.

Fuel is any flammable material surrounding a fire, including trees, grasses, brush, even homes. The greater an area's fuel load, the more intense the fire is likely to be. The most wildfire-prone state is California, which lost 259,148 acres of land to 8,194 wildfires in 2019.

Air supplies the oxygen a fire needs to burn. California wildfires are often made worse by the hot, dry Santa Ana winds, which can carry a spark for miles.

Heat sources help spark the wildfire and bring fuel to temperatures hot enough to ignite. Lightning, burning campfires or cigarettes, and even the sun can all provide sufficient heat to spark a wildfire.

Violent infernos are most common in the western states, where heat, drought, and frequent thunderstorms create ripe conditions. Montana, Idaho, Wyoming, Washington, Colorado, Oregon, and California experience some of the worst conflagrations. Wildfires also occur around the world and in most of the 50 states.

How they are stopped

Firefighters battle blazes by depriving them of one or more of the fire triangle fundamentals. One traditional method is to douse existing fires with water and spray fire retardants. Firefighters also sometimes work in teams, often called hotshots, to clear vegetation from the land around a fire to contain and eventually starve it of fuel. The resulting tracts of land are called firebreaks.

Firefighters may also employ controlled burning, creating backfires, to stop a wildfire. This method involves fighting fire with fire. These prescribed—and controlled—fires remove undergrowth, brush, and litter from a forest, depriving an otherwise raging wildfire of fuel.

Benefits of wildfires

Although they can be dangerous to humans, naturally occurring wildfires play an integral role in nature. By burning dead or decaying matter, they can return otherwise trapped nutrients to the soil. They also act as a disinfectant, removing disease-ridden plants and harmful insects from an ecosystem.

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High winds and hot temperatures fanned a 1996 wildfire in the foothills around Boise, Idaho, into an inferno that burned for seven days. When it was finally extinguished, the outbreak—dubbed the Eighth Street Fire—had scorched some 15,000 acres (6,000 hectares) and stripped bare two of the region's major watersheds.

Wildfires thin forest canopies and undergrowth, allowing sunlight to reach the forest floor and a new generation of seedlings to grow. In fact, some species of trees, like sequoias, rely on fire for their seeds to even open.

What to do in a wildfire

Wildfires devastate anything in their path. In 2018, the most destructive California wildfire of all time caused 85 deaths and was the world’s costliest single natural disaster that year with losses exceeding $16 billion. While they are difficult to stop, there are many steps people can take before, during, and after wildfires to limit their damage.


  • If you know a wildfire is traveling toward your area, the best thing to do is leave. Immediately.
  • If you live in a fire-prone area, its best to prepare for that course of action ahead of time. Have an evacuation plan in mind and a “go bag” with emergency supplies already packed during fire season.
  • Keep brush, weeds, and other potential fuels trimmed back on your property, especially around your home.
  • Put away grills, propane tanks, or other flammable materials that may be in your yard.
  • Close all doors and windows and fill sinks, tubs, and other containers with water to discourage fire.
  • Shut off natural gas, propane, or fuel oil supplies.
  • When you purchase a home in a wildfire-prone area, try to avoid neighborhoods on slopes that are steep or barren of vegetation, suggests the California Chaparral Institute. Although some people fear that houses near shrubs are more likely to burn, that’s not necessarily the case, the institute says. Rather, a landscape without vegetation can be the perfect runway for winds to bring embers, which are one of the biggest threats to homes during a wildfire.
  • Wetting your roof may help reduce the risk of airborne embers catching, says the California Chaparral Institute. In fact, some people in fire-prone areas even install rooftop sprinklers for that purpose.
  • If you cannot leave as a fire approaches, dial 911. Then don a face mask, or better, an N95 respirator to help reduce smoke and particle inhalation.


  • If you can still leave, leave.
  • Listen for emergency alerts.
  • If you cannot leave, stay inside. Go to the safest building or room with the lowest smoke levels. Crouch low for the best air. If you don't have a mask, breathe through a wet cloth.
  • If you are caught outside, try to find a body of water to crouch in. If you can't, find a depression with the least vegetation and lie low, covering yourself with wet blankets, clothes, or soil if possible.


  • Do not return until instructed to do so.
  • Listen to authorities before drinking water from the area.
  • Avoid items that are hot, smoky, or charred.
  • Text friends and family, but don’t call. Lines may be busy.
  • Wear a dust mask and document property damage.
  • Beware of the risk of flooding, since trees and protective vegetation might have been removed, exposing loose soil.